Being on LTE or 3G does not mean you will use more or less data.
No offense @mgriffs but this is the most stupid thing I have ever heard and not from you but what that "so called" technician spewed.... Honestly data is charged when accessing the internet via the apn. Switching from 3G to LTE back and forth won't cause your data usage to spike.
Your phone is using data for either app updates,software/firmware updates or there is a app that is open draining your data.
The High data ping values he is showing you.... What the hell is this? I think he is just showing you your daily usage graphs and has nothing to do with pining the network.... :erm:
Switching LTE off won't solve the issue since there is 3G towers with speeds faster than LTE so I doubt switching LTE off will solve anything. You should download a data monitor that you can see what is chowing your data. Most phones have this build in like android,iphone or windows phone. It shows stats and data usage by app which you can then limit,switch off or uninstall.
If this does not solve your issue I think you need to force your phone to 2G or downgrade to a phone that does not have internet.